1. Field of the Invention
The invention relates to electronic relays. More particularly, the invention relates to MOSFET based, high voltage, electronic relays for switching AC and DC power.
2. Description of the Prior Art
Advances in solid-state switching and relay technology have made possible the replacement of many electro-mechanical switching and relay assemblies. Solid-state devices provide the power control systems in which they are incorporated with long life, quiet operation and other associated advantages.
However, those skilled in the art will appreciate the difficulties associated with the development of electronic relays that may be used for AC power switching. Prior systems have exhibited shortcomings in the manner in which they provide for quick and reliable switching required in the management of AC power sources.
In addition to prior systems failing to provide for adequate switching required in the management of AC power sources, prior relays generally employ normally open contacts as opposed to the implementation of normally closed contacts. The use of normally open contacts results from the ready availability and ease of construction of semiconductor devices that restrict the flow of electricity (isolate power) in the absence of a control voltage or current. Prior to the development of the present invention, the implementation of normally closed contacts in a solid state relay would have required the inclusion of additional power inputs; something generally considered undesirable due to the added complexity and cost of the overall relay. Some prior art applications utilize depletion-mode MOSFETs to emulate normally-closed contacts. These applications are limited to extremely low current since the depletion-mode MOSFET has an inherently high resistance (typically a few ohms to 1000 ohms) compared to power MOSFETs with resistances as low as milli ohms. For high power applications, the depletion-mode MOSFET is not sufficient for carrying the required current.
With this in mind, the present invention overcomes the shortcomings of the prior solid state devices by providing a MOSFET based, high voltage, electronic relay for AC power switching and inductive loads. The present invention further provides a MOSFET based, high voltage, electronic relay for AC power switching which incorporates normally closed contacts without the need for the addition of power inputs as well as an override/bypass switch for use in conjunction with the relay such that a operator may selectively control operation of the relay apart from the automated controls of the relay.